1. Field of the Invention
The present invention relates to a procedure as defined in the preamble of claim 1 for scanning or disconnecting a transmission line in a V5.2 access node.
2. Description of the Related Art
There are at least two commonly known methods for connecting subscribers to a local exchange. In the first method, the subscriber is connected via a subscriber line directly to the local exchange or to an access module connected to it, while in the second method the subscriber is connected to an access network whose access node is connected to the exchange.
Open interfaces (V5.1 and V5.2) between an access network and a local exchange are defined in the ETSI (European Telecommunications and Standards Institute) standards of the ETS 300 324 and ETS 300 347 series. V5 interfaces enable subscribers belonging to a physically separate access network to be connected to a telephone exchange using a standard interface. In this application, V5 interface means expressly a dynamic concentrator interface (V5.2) consistent with the standards ETS 300 347-1 and 347-2, which consists of one or more (1-16) PCM (Pulse Code Modulation) cables. One PCM cable contains a total of 32 channels, each with a transfer rate of 64 kbit/s, i.e. 2048 kbit/s in all. The V5.2 interface supports analogue telephones as used in the public telephone network, digital subscriptions, such as ISDN (Integrated Services Digital Network) basic and system subscriptions as well as other analogue or digital terminal equipment based on semi-fixed connections.
Terminal devices can be connected to the subscriber ports of the access node. The access node can be provided with one or more V5 interfaces. Subscriber ports are created in the V5 interface by associating an unambiguous address of each port with a given address in the V5 interface. In the local exchange, this address is created as a V5 subscriber. In other words, each subscriber port has an address which is associated with a V5 address and which uses a given time slot or given time slots for signalling to the local exchange.
It is also possible to connect a subscriber module to the access node and connect the subscriber lines to the subscriber module. In addition, it is possible to connect a remote subscriber node to the access node e.g. via a PCM (Pulse Code Modulation) cable. In this case, the number of subscribers connected to the subscriber module or remote subscriber node may exceed the number of calls that can be transmitted simultaneously with the capacity of the interconnecting feeder between the subscriber module or remote subscriber node. In this situation it is therefore necessary to employ concentration even in the interconnecting feeder. This may further lead to a situation where it is not possible to establish a connection from a subscriber port through the subscriber module or remote subscriber node and the access node to the local exchange because there is no free time slot or module line in the interconnecting feeder for the subscriber port. In this case, call setup will fail.
In a V5 access node in a prior-art system, according to the standard, the part of the BCC protocol (Bearer Channel Connection; a protocol by which a transmission line can be reserved (PSTN) or connected (ISDN) in a V5.2 interface) associated with the local exchange scans and specifies a free time slot in the V5 interface and then transmits an ALLOCATION message to the part associated with the access node. After this, the part associated with the access node acknowledges receipt of the message by sending an ALLOCATION13 COMPLETED message. If the interconnecting feeder between the subscriber module or remote subscriber node is a concentrating one, a situation may occur where the capacity of the interconnecting feeder is insufficient for transmitting a call to a subscriber. Yet the call setup process in the local exchange advances on the basis of the ALLOCATION_COMPLETED message. When the call setup process has already reached an advanced stage, the access node attempts to scan a free time slot for the call, but the attempt may result in discovering that there is no free time slot and it is only then that the call setup is cancelled. Thus, the local exchange has reserved resources in the V5 interface, in the exchange itself and in the V5 access node for a call setup that fails because of insufficient capacity of the concent-rating interconnecting feeder.
The object of the present invention is to eliminate the problems described above. A specific object of the present invention is to present a new method for scanning a free module line or time slot from a connection formed from a V5 access node to a subscriber module or remote subscriber node at a correct and suitable stage with respect to call setup. A further object of the invention is to present a method that enables a subscriber module or remote subscriber node to be connected to a V5 access node via a concentrating link.
As for the features characteristic of the present invention, reference is made to the claims.
In the procedure of the present invention for scanning a module line or time slot in a V5 access node connected via a V5 interface to a local exchange and with a number subscribers connected to it via a concentrating link, a time slot in the V5 interface is scanned in accordance with the V5 standard by transmitting by means of the part of the BCC protocol associated with the local exchange, which may also be called a protocol object, a scanning message, such as an ALLOCATION message, to the part of the BCC protocol or protocol object associated with the V5 access node, which acknowledges receipt of the scanning message by issuing an ALLOCATION_COMPLETED message. In this context, scanning means a function or a series of functions designed to determine whether a line, channel or equivalent is free and available to the subscriber or call setup procedure. According to the invention, before receipt of the ALLOCATION message is acknowledged, i.e. before an ALLOCATION_COMPLETED message is transmitted, the concentrating subscriber interface is scanned to find a free module line or time slot, which is specified, preferably using the BCC protocol.
Once a module line or time slot is found, it is reserved for use in call setup and connected through the access node to the subscriber port indicated by the local exchange on the basis of the V5 interface time slot to be used, as indicated by the local exchange. Further, a route to the subscriber port indicated by the local exchange is determined, the specified module line or time slot is announced to the protocol controlling the call setup and a through connection is carried out to establish a user channel between the local exchange and the subscriber port. This ensures that while a time slot is reserved in the V5 interface, a free time slot or module line is also available for the call for further connection from the access node.
Depending on the application, the user channel may be a PSTN user channel, in which case subscribers are connected to the access node via an analogue connection and the switching of the module line is performed using the PSTN protocol, which transmits the signalling of analogue subscribers in the V5 interface. Further, the user channel may be an ISDN B-channel, in which case subscribers are digitally connected to the access node and the BCC protocol is used for the switching of the time slot.
Further, in an embodiment of the invention, a user channel set up by analogue or digital means can be disconnected via operations according to the invention. When a PSTN user channel is to be disconnected, the subscriber port reservation data are deleted via the BCC protocol and the link is disconnected via the PSTN protocol. When an ISDN user channel is to be disconnected, the subscriber port reservation data are deleted and the link is disconnected via the BCC protocol.
Depending on the application of the present invention, subscribers can be connected to a V5 access node via a remote subscriber node connected to it via a concentrating link. In this case, in practice subscribers are first collected into a network element of the remote subscriber node, which network element is connected to the access node e.g. via a PCM cable. On the other hand, subscribers can be connected to a V5 access node via a subscriber module connected to it via a concentrating link. Generally, the subscriber module is physically located in the same place as the access node, in which case a number of subscribers are connected to the subscriber module and the subscriber module is connected via a concentrating link to the access node.
As compared with prior art, the present invention has the advantage that the invention allows subscribers to be connected to an access node via a remote subscriber node or a subscriber module in addition to direct subscriber port connection in the access node. This also results in cost savings because it obviates the need to connect each subscriber to the access node via a separate cable.
A further advantage of the present invention is that the scanning of the concentrating interconnecting feeder is performed as early as possible, e.g. at the same time when a free time slot is reserved in the V5 interface, which means that resources of both the local exchange, the V5 interface and the access node are made available for other use if it is discovered that a call from the access node to the subscriber can not be set up.